Track rollers are rotatably mounted on a pair of sub-frames, mounted on either side of a track-type tractor, to support the tractor's main frame on a pair of endless track assemblies. The rollers are subjected to heavy loads during tractor operation primarily occasioned by the substantial weight of the tractor as well as its normal use over uneven and hard terrain. Such loading problems and solutions therefor are disclosed in U.S. Pat. Nos. 2,393,369; 2,775,492; 3,336,087; 3,695,737; and 3,774,708. The latter three patents are assigned to the assignee of this application.